What's Really In Our Gasoline?

Do you actually know?

By
Matt Jancer

Aug 23, 2016

Getty ImagesScott Olson

Last month the American Automobile Association put out a press release saying major fuel retailers's gasoline was significantly better for engines than that of the other two-thirds of gas stations in the U.S. It said half of American drivers don't regularly buy gas that contains top-shelf detergents, and our first thought was "Why would they? Nobody even says what these detergents are, and everybody's lost in a sea of marketing speak." We all see Shell advertising V-Power, Citgo droning on about TriCLEAN, and BP hawking Invigorate, but are they any better than Sunoco, Murphy, and Hess? AAA says they are, because they're three of 46 fuel brands part of the voluntary TOP TIER fuel standard.

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Gasoline comes with a lot mixed into it already: metal deactivators and antioxidants to keep it from separating into gum and liquid, oxygenates to make it burn more completely, and corrosion inhibitors. And then fuel retailers add to that detergent packages which prevent gasoline particles from building up in cars's fuel systems. It takes a mix of detergents to create a package that protects a whole fuel system. Polyether amine detergents do a good job on the engine's combustion chambers, where fuel and air mix, explode and turn the engine, PIB-amines and PIB-Mannichs work on the intake valves that draw in fresh air, and PIB-succinimides take care of the fuel injectors that spray gasoline into the combustion chambers.

The AAA report says, in layman's terms, "It is generally believed that the detergent is responsible for preventing deposit formation by adhering to the metal surfaces and forming a thin film." They don't sound too sure of the "why," but they're damn certain it works. They tested three TOP TIER fuels and three non-TOP TIER fuels on a Ford 2.3L port-fuel-injected I4 test engine for 100 straight hours to simulate 4,000 miles of driving. AAA calls the engine an industry standard for gasoline testing because the orientation and temperature of the intake valves during operation accelerate deposit formation more so than most engines, making it a tough engine to keep clean. Ford's sure pleased to hear that.

Intake valves are especially touchy; AAA found non-TOP TIER gasoline deposited 19 times as much buildup onto the test engine's intake valves. They also found that using TOP TIER fuel reversed much of that buildup within 1,000 simulated miles of driving. "Given the general similarity of internal combustion engines," says the report, "one can assume that engine carbon deposits formed using (non-TOP TIER) gasoline can, in most cases, be largely removed by switching to a gasoline that meets TOP TIER standards."

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It's worth pointing out, as it was worth us asking, that AAA and TOP TIER say neither contributes to the other financially and that AAA alone paid for and commissioned the test, which was performed by a third-party lab.

But the other two criteria – deposits on the cylinder piston top and cylinder head – didn't much vary from TOP TIER to non-TOP TIER fuel. A few TOP TIER fuels even tested very slightly worse on cylinder head deposits. Taking it all into account, though, TOP TIER seems worth it because, according to the AAA report, it performs so much better on intake valves and roughly the same elsewhere.

"Detergents have been used in gasoline since the early 1900s," says Greg Brannon, AAA's director of automotive engineering, "however, fuel companies began aggressively marketing detergents in the 1970s." There was no mandated threshold for detergents until the Environmental Protection Agency drafted the Lowest Additive Concentration (LAC) for gasoline in 1996. Car makers thought it was weak.

"General Motors, BMW, Honda, and Toyota worked together after the ruling of EPA LAC because the LAC rule is not adequate for proper engine deposit control," says a TOP TIER spokesperson. The program licensed its first fuel retailers in 2004. Volkswagen, Audi, Fiat Chrysler Automobiles, and Mercedes-Benz joined as partners later.

All the 46 major fuel retailers cited are part of the TOP TIER fuel program; exact detergents and blend rates vary from brand to brand. "While blending may vary, this difference can be as little as one quart versus four quarts of additive per 9,000 gallons of gasoline," says Brannon. All octanes have to contain the detergent blend to be licensed as TOP TIER.

AAA tracked nationwide prices for 39 fuel brands over 12 months and found that TOP TIER gasoline tended to cost three cents more per gallon, likely because fuel companies have to pay an annual per-station license fee to be certified in it, which funds TOP TIER. "A recent addition to the TOP TIER program is the requirement that all TOP TIER fuel marketers post the TOP TIER logo so that it is visible to consumers at the point of sale," says the fuel program whose name escapes us. So if you're swayed by the AAA, it's just become easier to spend that extra half-buck for a tank and a bit'a peace of mind.

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